The boy's parents, police and neighbors began a neighborhood canvass after his parents realized he was no longer in the yard.

Police said a neighbor found the boy's toy shovel a block away from his home, and authorities feared he had been abducted. But at 6:30 p.m., a resident in the 3600 block of Buckthorne Lane called police and said she heard a child crying, and the noise seemed to be coming from of a nearby storm sewer.

When police arrived, they discovered Alex in the sewer. Officers lifted the sewer's heavy grate, and Downers Grove Patrol Officer Russell Rau crawled into the duct and lifted the child to safety.

The boy was taken to Good Samaritan Hospital in Downers Grove for an exam, where doctors said his brief underworld visit had done him no physical harm.

But authorities were baffled as to how the boy got underground.

"We have no idea how he got there," Police Lt. David Rechenmacher said Monday. "He didn't tell us."